This study is designed to evaluate the inter-relationships between dispersal and other population regulatory mechanisms of the prairie vole, Microtus ochrogaster. The following basic information will be available: demographic changes in the population, fluctuations in the physical environment, changes in quantity and quality of the vegetation, energy requirements and availability, socio-physiological stress indicators, levels of aggressiveness, and changes in allelic frequencies within the population. Rate of dispersal from a 1 ha enclosed population will be monitored through recording one-way gates. Dispersing animals will also be captured to compare physiological condition, activity and movement patterns, level of aggressiveness and genetic "markers" of dispersers and nondispersers. Similar comparisons of dispersers and nondispersers will also be available from studies of voles dispersing into isolated habitat patches. Correlations of qualitative differences between dispersers and non-dispersers will aid in identification of stimuli triggering dispersal as well as evaluation of the significance of dispersal as a population regulatory mechanism.